In particular, the present invention is a fluid ejection device having an integral filter, and a method of forming such a fluid ejection device.
Throughout the business world, thermal ink jet printing systems are extensively used for image reproduction. Ink jet printing systems use cartridges that shoot droplets of colorant onto a printable surface to generate an image. Such systems may be used in a wide variety of applications, including computer printers, plotters, copiers and facsimile machines. For convenience, the concepts of the invention are discussed in the context of thermal ink jet printers. Thermal ink jet printers typically employ one or more cartridges that are mounted on a carriage that traverses back and forth across the width of a piece of paper or other medium feeding through the ink jet printer.
Each ink jet cartridge includes an ink reservoir, such as a capillary storage member containing ink, that supplies ink to the printhead of the cartridge through a standpipe. The printhead includes an array of firing chambers having orifices (also called nozzles) which face the paper. The ink is applied to individually addressable ink energizing elements (such as firing resistors) within the firing chambers. Energy heats the ink within the firing chambers causing the ink to bubble. This in turn causes the ink to be expelled out of the orifice of the firing chamber toward the paper. As the ink is expelled, the bubble collapses and more ink is drawn into the firing chambers from the capillary storage member, allowing for repetition of the ink expulsion process.
To obtain print quality and speed, it is necessary to maximize the density of the firing chambers and/or increase the number of nozzles. Maximizing the density of the firing chambers and/or increasing the number of nozzles typically necessitates an increase in the size of the printhead and/or a miniaturization of printhead components. When the density is sufficiently high, conventional manufacturing by assembling separately produced components becomes prohibitive. The substrate that supports firing resistors, the barrier that isolates individual resistors, and the orifice plate that provides a nozzle above each resistor are all subject to small dimensional variations that can accumulate to limit miniaturization. In addition, the assembly of such components for conventional printheads requires precision that limits manufacturing efficiency.
Printheads have been developed using in part manufacturing processes that employ photolithographic techniques similar to those used in semiconductor manufacturing. The components are constructed on a flat wafer by selectively adding and subtracting layers of various materials using these photolithographic techniques. Some existing printheads are manufactured by printing a mandrel layer of sacrificial material where firing chambers and ink conduits are desired, covering the mandrel with a shell material, then etching or dissolving the mandrel to provide a chamber defined by the shell.
In print cartridges typically used in thermal ink jet printers, a filter element is generally placed at the inlet of the standpipe against the ink reservoir (i.e., capillary storage member). The filter element acts as a conduit for ink to the inlet of the standpipe and prevents drying of ink in the capillary storage member adjacent the inlet of the standpipe. In addition, the filter element precludes debris and air bubbles from passing from the ink reservoir into the standpipe and therefrom into the printhead. Without a filter element, debris and/or air bubbles could enter the printhead and cause clogging of the ink flow channels, conduits, chambers and orifices within the printhead. This clogging is likely to result in one or more inoperable firing chambers within the printhead, which would require that the ink jet print cartridge, with the clogged printhead, be replaced with a new ink jet cartridge before the ink in the clogged cartridge is exhausted. From the perspective of cost, this course of action is undesirable.
The filter element within the ink jet print cartridge also helps to prevent pressure surges and spike surges of ink from the ink reservoir to the standpipe. A pressure surge of ink occurs upon oscillation of the print cartridge during movement of the carriage of the printer. A pressure surge can cause ink to puddle within the orifices of the firing chambers. This puddled ink can dry up clogging the firing chambers. A spike surge of ink occurs when the ink jet cartridge is jarred or dropped. In a spike surge, ink is rapidly displaced within the ink jet cartridge, which could allow air to be gulped into the firing chambers of the printhead, causing these chambers to de-prime. In these instances, the filter element, because it restricts ink fluid flow, helps to prevent unwanted puddling of ink within the nozzles and/or depriming of the firing chambers. However, since the filter element is rigid and positioned at the inlet of the standpipe, the filter element is somewhat ineffective for preventing pressure surges and spike surges for the ink within the standpipe itself
One aspect of the present invention provides a fluid ejection device. The fluid ejection device comprises a substrate, a stack of thin film layers and a further substrate. The substrate has a first surface and a second surface, and defines a fluid supply conduit. The stack of thin film layers has a first surface and a second surface, with the first surface of the stack of thin film layers being affixed to the second surface of the substrate. In one embodiment, the stack of thin film layers includes at least one fluid energizing element, and defines a plurality of fluid filter openings in fluid communication with the fluid supply conduit of the substrate. The fluid filter openings function as a fluid filter. The further substrate has a first surface coupled to the second surface of the stack of thin film layers, and an exterior second surface. The further substrate defines at least one firing chamber positioned over the at least one fluid energizing element of the stack of thin film layers, with the firing chamber opening through a nozzle aperture in the exterior second surface of the further substrate.